• Fig. 4.8 Diagram of the spinal cord, spinal roots, and spinal nerve. The spinal nerve begins where the dorsal and ventral roots fuse, and has multiple branches (rami), the first few of which are represented. A primary afferent neuron is shown with its cell body in the dorsal root ganglion and its central and peripheral processes distributed, respectively, to the spinal cord gray matter and to a sensory receptor in the skin. An α motor neuron is shown to have its cell body in the spinal cord gray matter and to project its axon out the ventral root to innervate a skeletal muscle fiber.
CHAPTER 4 The Nervous System: Introduction to Cells and Systems
Massa intermedia of Thalamus Interventricular foramen Fornix Anterior commissure Infundibular recess Lamina terminalis
Choroid plexus of third ventricle •Fig. 4.9 Midsagittalviewofthebrainshowingthethirdandfourthventricles,thecerebralaqueductofthemidbrain,andthechoroidplexus.TheCSFformedbythechoroidplexusinthelateralventriclesentersthiscirculationviatheinterventricularforamen.Notealsothelocationofthecorpuscallosumandothercommissures.(FromHainesDE[ed]:Fundamental Neuroscience for Basic and Clinical Applications. 3rded.Philadelphia:ChurchillLivingstone;2006.)
The thalamus sits at the upper end of the brainstem and is enclosed by the cerebrum with which it is highly interconnected (see
Fig. 4.6B ). With a few exceptions, ascending information first reaches the thalamus, which conveys it to the cerebral cortex. These structures play a major role in many functions, including conscious awareness, volition, memory, and language. In addition to the cortex, the cerebrum contains a group of deep nuclei, the basal ganglia, that are interconnected with the cortex and thalamus and whose function will be described in
The major functions of the different parts of the CNS are listed in
Table 4.1
CSF fills the ventricular system, a series of interconnected spaces within the brain, and the subarachnoid space directly surrounding the brain. The intraventricular CSF reflects the composition of the brain’s extracellular space via free exchange across the ependyma, and the brain “floats” in the subarachnoid CSF to minimize the effect of external mechanical forces. The volume of CSF within the cerebral ventricles is approximately 30 mL, and that in the sub-arachnoid space is about 125 mL. Because about 0.35 mL of CSF is produced each minute, CSF is turned over more than three times daily.
CSF is a filtrate of capillary blood formed largely by the choroid plexuses, which comprise pia mater, invaginating capillaries, and ependymal cells specialized for transport. The choroid plexuses are located in the lateral, third, and fourth ventricles (see